This application is directed generally to apparatus for collecting fluid samples, and more particularly to a syringe for collecting a blood sample from a human or animal blood vessel.
One method commonly used for collecting blood samples from the artery of a human is to puncture the artery by means of a conventional syringe needle with the piston of the syringe in an advanced position, and thereafter retract the piston to suck a blood sample into the chamber of the syringe. However, it is not always possible to ascertain whether an artery has been actually punctured before retracting the cylinder, with the result that the patient may be subject to discomfort and inconvenience as another attempt is made to puncture the artery. Furthermore, even after an artery has been punctured, it is difficult to keep the syringe still as the piston is retracted, with the result that the patient may experience further discomfort during the procedure.
An alternative procedure for collecting a blood sample utilizing a syringe is described in U.S. Pat. No. 3,943,917. This procedure contemplates that the piston of the syringe be prepositioned to form a collection chamber within the syringe. The syringe needle is then inserted into an artery, and blood from the artery is allowed to flow into the chamber while the piston remains stationary. A passageway formed by either a channel in the syringe housing or by the insertion of a wedge member in the form of a rod or tube to deform the piston seal allows air to escape from the chamber as blood enters the chamber. When the chamber has filled, the passageway is closed by repositioning the piston or by removing the wedge member, and the sample is dispensed as required by advancing the piston.
One disadvantage of this alternative procedure has been the necessity of the operator having to close the air escape passageway following collection of a blood sample. Where the passageway is formed in the syringe housing, this has necessitated advancing the piston to a position clear of the passageway, thereby decreasing the volume of the chamber and causing an undesired dispensing of blood through the syringe needle. Where the escape passageway is formed by deformation of the piston seal, the operator is required to locate and withdraw the wedge member after the wedge member has been in contact with the collected blood sample.
One proposed solution to the problem of closing the air escape passageway provides a length of string along one side of the piston to displace the piston seal. The outside end of the string is wound around the piston stem, which is rotatably mounted to the piston. To remove the string and thereby seal the collection chamber, the stem is twisted by the operator until the string is drawn clear of the piston seal. Like the previously described syringe apparatus, this apparatus requires attention and manipulation by the operator, and presents a risk of leakage as the string is removed.
The syringe apparatus of the present invention avoids the necessity of the operator having to manipulate the syringe to seal the collection chamber by providing an air relief passageway which is automatically closed upon the collection chamber filling with blood. This is done without attention by the operator, and without the possibility of leakage.